This invention relates to cutting concrete to prevent cracks.
Concrete is formed of a combination of a hydraulic cementing substance, aggregate, water, and, often other substances to impart specific properties to the concrete. When concrete is poured it is typically in a watery or flowing state which allows the concrete to be spread evenly over floors. After a period of time, varying with the mixture of the concrete, the temperature, and the moisture availability, the concrete attains a workable plasticity which permits the surface of the concrete to be formed and to retain a finish. Typical finishing means include troweling rubbing, or brushing. Applying the desired surface texture is called "finishing" the concrete, and may involve repeated steps to sequentially refine the surface finish.
After the concrete is finished, it is allowed to stand for a period of time during which the concrete cures to obtain its well-known, rock-like hardness. The curing or setting time depends on the moisture available, the temperature, and the specific additives added to the concrete to affect the curing time. As the concrete cures it shrinks, which causes cracks. Thermal stresses from weather variations can also cause cracking.
It is common practice to provide slots or grooves at predetermined intervals in the concrete for crack control. Even if grooves are only on the surface of the concrete, the grooves cause the cracks to form along the bottom of the grooves so that they occur at regular intervals and are not visible. The grooves, but not the cracks, are visible. Of course the grooves must be put in the concrete soon enough or else all of the cracks will have already formed, and the grooves will be of no use.
U.S. Pat. Nos. 4,889,675 and 4,769,201, both to Chiuminatta, et. al., discuss a method of cutting uncured concrete by in part, controlling the spacing between a rotating concrete cutting blade and the adjacent sides of a skid plate. Using the method of cutting described in these Chiuminatta patents, a common specification for cutting grooves is to cut them 5/8 to 1 inch deep, and about 0.1 inch wide, with the cutting occurring within a few hours after the concrete is finished.
The crack control grooves may also function as contraction joints. Typically, a slab of concrete is at its largest size when it is poured, and it shrinks or contracts thereafter. As the concrete shrinks, the slabs of concrete on each side of the groove contract and the grooves widen. When the temperature rises, the grooves may partially close. Since the grooves accommodate the contraction of the concrete, they are called contraction joints even though the grooves themselves sometimes spread apart, or expand.
In outdoor applications it is common practice to seal these contraction joints by sealing the grooves with tar or other sealants. The sealants prevent water from entering the cracks at the bottom of the grooves, soaking through to the bottom of the concrete, and creating a weakened spot in the foundation, or even washing away the foundation of the concrete. Moisture freezing in the cracks can also gradually widen the cracks. The sealants can only stretch a limited amount, and thus can accommodate only a limited amount of widening of the grooves before the sealants pull away from the sides of the grooves and allow moisture to pass into the groves and cracks. Currently, a sealant segment about 0.25 inches (0.635 cm.) square is needed to accommodate the width changes which occur in the grooves, with some sealant suppliers preferring about 0.375 inches (0.9525 cm.) square or more of sealant.
Since the crack control grooves are typically much smaller, on the order of 0.09 inches (0.020574 cm.), a larger and shallower groove, called a "well," is cut into the top of the crack control grooves and sealant placed into the well. The groove forming the well for the sealant is typically 0.25 .times.0.25 inches, or 0.375.times.0.375 inches.
Conventional practice has been to cut crack control grooves in the concrete as soon as possible, and about 7 days later, to use diamond abrasive water saws to cut over the crack control grooves and form a wider, shallower well into which the sealant is placed. Since the sealant well is so much wider than the crack control grooves, the concrete must be allowed to become very hard to avoid cracking, chipping, and spalling of the concrete when the 0.25 or 0.375 inch wide groove is cut to form the well for the sealant. Thus, the seven day delay is often required to insure the concrete is sufficiently hard and will not crack, chip, or spall when the wide groove for the sealant well is cut in the surface of the concrete.
It is very costly and time consuming to cut these grooves for the sealant so long after the concrete is poured, as it requires sending workers back to locations which are often far away from where the main work force is then employed. Moreover, the water abrasive saws are bulky and heavy, weigh 900 pounds or more, and require a water source and water hoses to lubricate the saw. The cutting also splatters a lot of concrete mud and water, and causes a time consuming cleanup.
The slurry created by the water lubricated saws also imbeds particles in the sides of the cut groove which prevent the sealant from properly sealing. Thus, it is common practice to sandblast the cut grooves to remove this imbedded slurry. The extra time, labor, and equipment are again expensive and cumbersome to provide.
There is thus a need for an improved method and apparatus to cut concrete and form crack control grooves, and to cut grooves to form wells for sealants. There is a further need for cutting such grooves with the least time and labor necessary, while still producing grooves of acceptable, if not superior, surface finish by providing grooves without any cracking, spalling, or chipping along the edges of the groove. There is a further need to provide a smaller and lightweight way to cut these wells for the sealants, and to do so without the water connections, water consumption, sandblasting, and mess associated with conventional, diamond abrasive water saws.